Thermal liquefaction of coal

ABSTRACT

A SUB-BITUMINOUS COAL IS LIQUEFIED BY RAPIDLY HEATING SLURRY OF SAID POWDERED COAL IN A HYDROGENATED SOLVENT AT A TEMPERATURE RANGE OF FROM 440* TO 450*C., AND A RESIDENCE TIME OF FROM ABOUT 5 TO 20 MINUTES.

."United States Patent 01 hoe 3,594,304 THERMAL LIQUEFACTION F COAL Walter H. Seitzer, West Chester, and Robert W. Shmn,

Chester, Pa., assignors to Sun Oil Company, Philadelphia, Pa. N0 Drawing. Filed Apr. 13, 1970, Ser. No. 27,975 Int. Cl. C10g 1/04 US. Cl. 208-8 4 Claims ABSTRACT OF THE DISCLOSURE A sub-bituminous coal is liquefied by rapidly heating a slurry of said powdered coal in a hydrogenated solvent at a temperature range of from 440 to 450 C., and a residence time of from about 5 to 20 minutes.

Numerous coal liquefaction processes are well known in the art. For example, US. 2,686,152 discloses a lignitic coal extraction process carried out with an organic solvent such as Tetralin or a mixture thereof with a phenol at temperatures between about 480 F. (249 C.) and about 900 F. (482 C.), preferably between 750 F. (399 C.) and about 860 F. (460 C.), with or without hydrogen being used, and at atmoshperic or at autogenous hydrogen pressure, said extraction process being carried out without any particular attention being paid to time of reaction and generally a time of about 30 minutes to 1 hour being preferred. This prior art disclosure indicates that liquid products are formed in an amount ranging from about 7% to about 50%. Gas formation is also observed in an amount varying from 13% to 28% by weight of total products, the remaining products being mostly coke or char. Such a procedure cannot economically lend itself toward commercial production of liquid products. What is needed in any commercial coal liquefaction process is essentially complete liquefaction of the coal with minimum formation of gaseous products, since these gases are of little economic value and are in effect waste products which consume valuable hydrogen.

A new coal liquefaction process for sub-bituminous coal has now been found which is able to achieve solution of 90% or more of the coal and which minimizes gas production. This is accomplished in accord with this invention by subjecting a sub-bituminous coal to solution in a hydrogenated poly-nuclear solvent under pressure of hydrogen of from about 2000 to about 3000 p.s.i.g. and maintaining the temperature of the process within the narrow range 440 to 450 C. for a period of about 5 to about 20 minutes residence time. In view of the knowledge of the art, it is indeed surprising to find that the critical conditions of the process make possible a significant increase in amount of coal dissolved and in minimizing the amount of gaseous products formed.

As indicated, the coal used in the process of the invention will be a sub-bituminous coal and this will include lignite coals such as North Dakota lignite, Powder River Sub-bituminous Coal, and the like.

The solvent used in the process will be a hydrogenated poly-nuclear solvent freqently known as a hydrogen donor solvent. These donor solvent materials are well known and comprise aromatic hydrocarbons which are at least partially hydrogenated, generally having one or more of the nuclei saturated or partially saturated. Several examples of such materials are Tetralin, dihydronaphthalene, dihydroalkylnaphthalene, dihydrophenanthrene, dihydroranthracene, dihydrochrysene, tetrahydrochrysene, tetrahydropyrene, tetrahydrofiuoranthene and the like. Of particular value in the process of this invention as hydrogen donor solvents are the hydrophenanthrenes and hydroanthracenes such as dihydroanthracene. It will be understood that these materials may be obtained from any source, but are readily available by partially hydrogenating appropriate aromatic products by conventional techni ques. Specific preferred examples of such materials are anthracene oil and Tetralin. In the preferred process the solvent used will be a distillate fraction of the dissolved coal which has been hydrogenated by any standard commercial technique. The amount of solvent used in the process may vary, but enough must be used to provide a stirrable slurry. Usually the amount of solvent used will be a weight ratio of oil to coal of about 1:1 to 5: 1.

The preferred parameters of the process are a temperature of 445 to 450 C., a pressure of about 2500 p.s.i.g., a solvent to coal ratio of about 2:1, and a residence time of 10 to 20 minutes.

In carrying out the process of the invention, a slurry of the powdered coal in the hydrogen donor solvent is introduced into a pressure reactor and the reactor is pressured with hydrogen to a pressure of from about 1000 to about 1500 p.s.i.g. As the contents of the reactor are stirred or agitated, the temperature is raised rapidly to the critical temperature range of 440 to 450 C., and the pressure rises to between about 2000 and 3000 p.s.i.g. In raising the temperature care must be exercised to avoid holding the reaction products at temperatures between about 400 and reaction temperature for any length of time. No significant solution or changes in the coal will occur below about 400 C., but when the reaction mass reaches the 400 C. range, then the rise in temperature to 440 to 450 C. must be rapid, say within a few minutes, in order to avoid chemical changes in the coal which will reduce its conversion to soluble products. On the other hand, if the temperature goes above 455 C., recoking of the coal liquid occurs and thus solubility is drastically reduced. As also indicated, the time used for the process is critical and residence time at a temperature of 440 to 450 C. is preferably between about 10 and about 20 minutes. If a residence time of less than about 5 minutes is used, solubility is again reduced to an impractical amount. On the other hand, if operation is continued for more than about 20 minutes, then the formation of gases such as methane, ethane, and propane are so great as to significantly reduce the efficiency and economics of the process. After the solution is completed in accord with the above steps, heating is stopped and the products are filtered hot or, optionally, cooled before filtering.

It is also unexpected that the process must be carried out in a single stage. It would be thought that hydrocarbon gas formation could be kept to a minimum by employing a two step system; i.e., partial liquefaction at a low temperature (say about 425 to 435 C.) and then final and more complete liquefaction at a higher temperature (about 450 C.). However, it is found that such two stage operation results in coking and much lower solution being obtained. Thus, only the very narrow critical conditions of the process give the high coal solubility necessary for a satisfactory commercial process.

The dissolved coal formed by the process of the invention is a valuable product similar in many respects to a crude oil and is subjected to the usual refining operations to produce petroleum products. For use in this manner, the solution is merely filtered to remove the small amount of insoluble products present, and the filtrate treated in accord with conventional refinery techniques.

In order to more fully describe the invention, the following examples are given:

Liquefaction of coal was carried out in stirred pressure reactors which contained powdered Big Horn Coal and TABLE I Final Percent Hydrocarbon Time, pres, organic gases, wt. permins. p.s.i.g. dissolved cent of coal Following the experimental details set forth above, the time of reaction was varied. The results are shown in Table II which follows.

As can be seen from the above table, the reaction time is critical to the amount of coal dissolved and to the amount of hydrocarbon gases evolved. Maximum solubility of coal and minimum evolution of gases occurs at about 20 minutes of reaction time within the critical temperature range. When more than about 20 minutes residence time is permitted yield of unwanted hydrocarbon gases increases significantly.

The need for a hydrogenated oil in the process of the invention is shown in Table III where it is seen that when an unhydrogenated anthracene oil is used the coal solubility dropped to 41%.

TABLE III.THERMAL LIQUEFACTION OF COAL Unliydrogenated anthraeene oil.

The effect of pressure in the process is observed in the results set forth in Table IV. Here it is observed that pressures below about 2500 p.s.i. significantly reduce the amount of coal solution.

TABLE IV Final Percent Hydrocarbon Time, pres, organic gases, wt. per- Temp., 0. mins. p.s.i.g. dissolved cent of coal As indicated, the process of the invention is also dependent upon use of a single step procedure. Thus, liquefaction at a lower temperature subsequently followed with a higher temperature cause coking and greatly decreases the amount of coal solution to the range. Likewise, the high temperature in the second step causes a large amount of hydrocarbon gases to be formed. These results are seen in Table V.

TABLE V.THERMAL LIQUEFACTION OF COAL Final Percent Wt. percent Time, pres, organic coal yield Temp, 0. mins. p.s.i.g. dissolved HC gases & 4O 2,700 10 10.8 4 0. 20

It is thus clear from the above experimental details that the process of the invention is highly dependent upon the critical features of temperature, pressure, time of reaction and operating in a single stage. By following these critical parameters, high coal solubility is achieved in extremely short time thereby providing a very efficicnt and economical process.

The invention claimed is:

1. A liquefaction process for coal which comprises subjecting a sub-bituminous coal to solution in a hydrogen donor solvent under hydrogen pressure of about 2000 to about 3000 p.s.i.g. at a temperature of about 440 to about 450 C. for a period of about 5 to about 20 minutes.

2. A process for dissolving coal which comprises heating a slurry of a powdered sub-bituminous coal in a hydrogen donor solvent at a temperature of about 440 to about 450 C. under a pressure of hydrogen of about 2500 p.s.i.g. for a time from about 10 to about 20 minutes, whereby at least about by weight of said coal is dis solved and the amount of hydrocarbon gases formed is minimized.

3. The process of claim 2 wherein the hydrogen donor solvent is a hydrogenated anthracene oil.

4. The process of claim 2 wherein the hydrogen donor solvent is a distillate fraction of the dissolved coal which has been hydrogenated.

References Cited UNITED STATES PATENTS 2,714,086 7/1955 Bliiemner 208-8 3,143,489 8/1964 Gorin 2088 2,686,156 8/1954 Franke 208--8 2,658,861 11/1953 Pevere et al. 2088 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner 

